Yep, it's definitely available. You just need a keyboard that has a mic built-in. For some stupid reason, when the Eris updated to 2.1, it was promised as a feature, but the built-in keyboard has no mic button!!!

We started off with the HTC_IME mod apk. At the moment my wife is using Better Keyboard (beware, it's $2.99, but has lots of free skins), which seems to be a lot easier for her to type on than others we've tried. There's a good comparison at: